The disclosed subject matter relates to techniques for providing a frequency standard using spin states of a defect in a diamond structure.
Atomic clocks can serve as the basis for accurate systems in use for measuring time and frequency. They can be utilized in a number of applications, including communication, computation, mobile devices, sensors, autonomous vehicles, undersea oil/gas exploration, space navigation, aviation, cruise missiles, and navigation systems (e.g. global positioning systems (GPS)).
Certain frequency standards can derive their stability from hyperfine level splitting of energy states in atoms such as Cs, Rb, or H. When an oscillating magnetic field is resonant with the energy difference of these internal states, a change in population between levels changes the radiofrequency or optical absorption. Certain techniques can modulate the driving frequency and monitor the absorption as a correction for a tunable active reference oscillator, e.g. a quartz crystal, thus stabilizing it to the atomic line.
Single trapped ions and ensembles of atoms trapped in optical lattices can provide a frequency standard with accuracy exceeding the international cesium standard, and can enable the observation of general relativity corrections within a few meters. Such techniques, however, can require infrastructure that encompasses several tens of cubic meters of space.
Portable standards based on rubidium vapor cells can provide stability for time scales ranging from 1 s to 104 s and can be used in connection with satellites, laboratory equipment, and cellular communications. Mobile devices, which may not contain their own precision standards, can share GPS time signals for maintaining communication standards, but when the external lock signal is obstructed, a precise local frequency standard with minimal drift can be necessary to maintain synchronization.
Accordingly, there is a need for improved techniques for providing a frequency standard for time-keeping.
Nitrogen Vacancy Centers (NVC) are point defects in the diamond crystal structure. The substitution of a nitrogen atom for a carbon atom in the diamond structure can create a lattice vacancy that can be occupied by three unpaired electrons. In a neutral nitrogen vacancy defect, N—V0, two of the unpaired electrons can form a quasi covalent bond, while the third electron remains unpaired. However, the three electrons can exhibit axial symmetry, and the three continuously exchange roles. A negative nitrogen vacancy, N—V−, can have an additional electron associated with the vacancy which forms an S=1 structure that has a long-lived spin triplet in its ground state that can be probed using optical and microwave excitation. This can allow for spin manipulation of the NVC.
The NVC can have trigonal C30 symmetry and 3 A2 ground state with total electronic spin S=1. Spin-spin interaction can lead to a zero-field splitting between the ms=0 and ms=±1 manifolds, where the quantization axis is along the NV-axis. NVCs can have a crystal field splitting frequency (Dgs) of, for example, 2.870 GHz in the absence of an external magnetic field and in the absence of other environmental factors, including strain. This zero-field splitting frequency can be changed by the application of magnetic fields in the direction of the NVC through the Zeeman effect.